Inverter



ENVERTER Filed sept. 26 1945 Wei l? 6 MTPUT their low drain of controlpower.

Patented July 12, 1949 INVERTER Hans Klemperer, Belmont, .Mass.,assignor to Raytheon Manufacturing Company, Newton, Mass., a corporationof Delaware Application September 20, 1945, Serial No. 617,610

This invention relates to an electrical system for converting directcurrent into alternating current.

It is frequently desired to obtain a stabilized alternating voltage of agiven frequency from a direct current source of widely varying voltage.For example, where the direct current source is a storage battery, theinput voltage may vary considerably depending upon the condition andstate of charge of the battery. If the alternating current output mustbe relatively stable, it has heretofore been necessary to provide avoltage regulator to -control the output of the source.

It is among the objects of the present invention to provide a system inwhich the inverter itself functions t supply a highly stabilizedalternating current output without the necessity for interposing voltageregulator units.

It is a further object of the invention to provide a system of the typein which there are no moving parts throughout the power system.

It is a further object to provide a system of the type described inwhich the power losses are relatively low.

The above and other objects and features of the invention will be madefully apparent to those skilled in the art from a consideration of thefollowing detailed description taken in conjunction with theaccompanying drawing in which:

Claims. (Cl. 175-363) Fig. 1 is a diagrammatic representation of anstance shown, the control electrodes II and I2 are make-alive electrodesof the dielectric type, as described and claimed in U. S. Patent No.2,257,768 to Percy L. Spencer, patented October 7, 1941, and which areparticularly suited to the purposes of the present invention because ofHowever, it will be understood that other control elements, such asother types ofmake-alive electrodes or grids may -be utilized. The anode8 of the tube 6 is connected tothe positive terminal of a source ofdirect current I3. Its cathode I0 is connected to the vanode 'I of thetube 5, the cathode 9 of which tube is connected tothe negative terminalof the direct current source I3. A pair of condensers I4 and I5 areconnected in series across the terminals of the source I3. Acircuit,including a -condenser I6 and a saturable reactor I1 in paralleltogether with a linear reactor IB in series, is connected between apoint intermediate the condensers I4 and I5 and a point 1ntermediate theanode 1 of the tube 5 and the cathode III of the tube 6.

In order to supply energizing impulses to the control electrodes II andI2 of the tubes 5 and 6, I provide an energizing circuit comprising a.vibrator 20 having an armature 2| connected through an inductor 22 toone of the terminals of a source of direct current 23, for instance, asix-volt battery. The armature 2I is adapted to vibrate between contacts24 and 25 connected to the opposite ends of a primary winding 26 of apeaking transformer 21. A center tap on the primary winding 26 isconnected to the other terminal of the direct current source 23.Preferably, a condenser 28 is connected across the primary winding 26 ofthe peaking transformer 2l. A pair of secondary windings 29 and 30 areprovided on the peaking transformer 21, one terminal of the secondarywinding 29 being connected to the control electrode II of the tube 5,and the other terminal of this winding being connected to the cathode 9of the tube 5. The other secondary winding 30 of the peaking transformer21 similarly has one terminal connected to the control electrode I2 ofthe tube -B and its other terminal connected to the cathode I0 of saidtube. The stabilized alternating-current output may be led off fromterminals 3I, one of which is connected to the lower end of thesaturable inductor I'I, and the other terminal of which Yis connected toa tap 32 at `an adjustable point intermediate the length of the inductorII.

When the system described in the foregoing is energized, the condensersI4 and I5 are each charged to a voltage which is approximately half thevoltage of the direct-current source I3. When the vibrator circuit isclosed, an energizing impuke is supplied to one or the other of thecontrol electrodes II land I2 of the tubes 5 and 6. Assuming that theenergizing impulse is supplied by the secondary winding 29 of thepeaking transformer 2I to the control electrode II of the tube 5, thecondensers I4 and I5 change their charge through the parallel circuit,including the condenser I6 and inductor I1, the inductor I8 and the tube5.l The discharge circuit of the condenser I4 may not be highly damped,and therefore its discharge current may tend to be oscillatory. In suchcase, when the condenser I4 loses charge through the tube 5, its voltageis reversed. The magnitude of the reversed voltage is determined by thedegree to which energy is absorbed in the output circuit. Since thevoltage which is impressed on the condenser I5 is the sum of the voltageof the direct-current source and the voltage of the condenser I4, itwill be seen that upon the discharge of the condenser I4 the l condenserI is charged to a. higher potential than that of the direct currentsource.

During discharge of the condenser I4 and the further charging of thecondenser I5 in the manner described, the condenser I6 is charged insuch a direction that its lower 'end becomes positive and its upper endnegative. An inverse voltage is thus applied to the tube 5 due to thereversal of the charge on condenser I4 and also Idue to the direction ofthe charge on the condenser I6. The tube 5 goes out. The condenser i6discharges through the inductor I1 which becomes saturated. At a timewhen the charge on the condenser I6 has reversed so that its upper endis positive and its lowerend is negative, an energizing impulse issupplied to the ignitor I2 of the tube 6. This tube fires to dischargethe condenser I5 through the oscillatory circuit, comprising thecondenser I6 and the inductor I1 in the reverse direction to thedischarge of condenser I4, and thus recharges condenser I4 in itsoriginal polarity. The charge on the condenser I5 is applied across theinductor I1 in the same direction as the charge on the condenser I6. Avoltage is thus applied across the terminals of the inductor I'I, aportion of which voltage is applied across the terminals 3| of thealternating-current output circuit. After the saturation of the inductorII, the direction of the charge on the condenser I6 is again reversed,the lower side thereof again being positive, and the condenser I4 isagain charged in the original polarity. The potential across the outputterminals 3l is now reversed, the tube 5 is again discharged, and thecycle is repeated.

The circuit described in the foregoing provides a system in which ahighly stabilized alternating current output is obtained from a variabledirect current source even though the voltage of the source may varyover Wide limits. This effect is obtained in the following manner.

As previously stated, the voltage on the condensers I 4 and I5 deriveddirectly from the source I3 is one-half of the voltage of said source.However, upon the discharge of one of the condensers, the charge on theother condenser is increased. The voltage across the output terminals 3|is directly proportionalto the voltage across the oscillatory circuitIG-Il. It will be seen that without the inductor I8, upon the firing ofone of the tubes 5, the full voltage of the corresponding condenser I4,except for the small voltage drop across the tube 5, will be appliedacross the oscillatory circuit I6I'I. Accordingly, the voltage acrossthe output terminals 3I would vary directly with variations in thevoltage of the source I3.

With a non-saturable inductor IB in the discharge circuit of thecondensers I4 and I'5, upon the ring of one of the tubes, say 5, thefull voltage of the corresponding condenser I4 does not immediatelyappear across the oscillatory circuit IG-I'I due to the impedance of theinductor I8. On the contrary, the voltage rises gradually in a more orless sine-like Wave. If the inductor I'I were non-saturable, the voltageacross the inductor I'I would nevertheless vary with variations in thevoltage on the condenser I4. However, since the inductor I1 issaturable, once the current through it has passed the saturation value,the voltage thereafter does not build up on the condenser I6 except tothe degree permitted by the losses within this inductor. `Since theselosses are low, the voltage drop across it rises only gradually withincreases in current. It will thus be seen that, in the construction oithis invention, any tendency of the voltage across the condenser I4 toincrease will be counteracted by the parallel condenser I6. The outputvoltage is therefore highly stabilized regardless of variations in thevoltage of the source I3.

It will be understood that the frequency of the oscillatory circuitIS-I'I is not critical, that is to say, the natural frequency of theoscillatory circuit IB-I 1 may vary over a considerable range offrequencies in the region of the frequency oi the vibrator 20. Since theoscillations of the oscillatory circuit I6-I1 are forced by thealternate discharge of the condensers I4 and IB therethrough, thiscircuit will oscillate at the vibratory frequency of the vibrator 20even though its natural frequency may vary substantially therefrom. Theoscillatory circuit, however, is tuned to a lower frequency than theinverter circuit comprising the inductor I8 and the condensers I4 andI5. The energy from the inverter circuit is thus supplied to theoscillatory circuit in short impulses occurring during the initialportion of each alternation of the oscillatory circuit in a manner whichwill be apparent from a consideration of Fig. 2 of the drawing whichshows the current variations with respect to time. It will be understoodthat this gure is not intended to represent the variations in aquantitative sense but does represent the variations in a generalqualitative manner. The oscillations of the oscillatory circuit IS--I'Iare indicated by the curve I0, and the oscillations of the invertercircuit I4-I5-I8 are indicated by the curves Il.

The damping load in the oscillatory circuit IS-I'I is low, so that thecirculating power is high relative to the load. The circuit thusprovides a system in which the alternating current output is stabilizedover a wide range of direct current input voltages.

It will be understood that the inverter is primarily intended to supplya resistance load, since a load having an inductive or capacitiveimpedance will reflect this impedance into the oscillatory circuit ofthe inverter, and thus change the output voltage to which the circuit iscalibrated.

Preferably, the output frequency as determined by the frequency of thevibrator 20 will be as high as heat losses in the saturated componentwill allow, since with increasing frequency the size of the inductorsand capacitors may be decreased.

While there has been herein described a preferred embodiment of theinvention, other embodiments within the scope of the appended claimswill be obvious to those skilled in the art from a consideration of theform shown and the teachings hereof. Accordingly a broad interpretationof the appended claims commensurate with the scope of the inventionWithin the art is desired.

What is claimed is:

1. An inverter comprising a source of voltage, a rst condenser connectedacross said source of voltage, an oscillatory circuit comprising asecond condenser and a saturable inductor, a discharge circuit fordischarging said iirst condenser through said oscillatory circuit, acontrolled ignition discharge tube in said discharge circuit for causingsaid rst condenser to discharge, a linear inductor in said dischargecircuit, means for timing the ignition of said discharge tube to controlthe discharge of said first condenser through said 'ing said firstdischarge circuit, and means to derive an alternating output currentfrom said oscillatory circuit.

2. An inverter comprising a source of voltage, a iirst condenserconnected across said source of voltage, an oscillatory circuitcomprising a second condenser and a saturable inductor, a dischargecircuit tuned toA a higher frequency than said oscillatory circuit fordischarging said first condenser through said oscillatory circuit, acontrolled ignition discharge tube in said discharge circuit for causingsaid first condenser to discharge, a linear inductor in said dischargecircuit means for timing the ignition of said discharge tube to controlthe discharge of said first condenser through said discharge circuit,and means to derive an alternating output current from said oscillatorycircuit.

3. An inverter comprising a source of voltage, a iirst condenserconnected across said source of voltage, an oscillatory circuitcomprising a second condenser and a saturable inductor, a dischargecircuit for discharging said rst condenser through said oscillatorycircuit, a space discharge tube in said discharge circuit for causingsaid first condenser to discharge, a linear inductor in said dischargecircuit, means for timing the discharge of said tubeto control thedischarge of said first condenser through said discharge circuit, andmeans to derive an alternating output current from said oscillatorycircuit.

4. An inverter comprising a source of voltage, a first condenserconnected across said source of voltage, an oscillatory circuitcomprising a second condenser and a saturable inductor, a dischargecircuit for discharging said first condenser through said oscillatorycircuit, a space discharge tube in said discharge circuit forcauscondenser to discharge, a linear inductor in said discharge circuit,a vibrator for timing the discharge of said tube to control thedischarge of said first condenser through said discharge circuit, andmeans to derive an alternating output current from said oscillatorycircuit.'

5. An inverter comprising a source of voltage, a first condenserconnected across said source of voltage, an oscillatory circuitcomprising a condenser and a saturable inductor, a discharge circuit fordischarging said iirst condenser through said oscillatory circuit, saiddischarge circuit being tuned to a higher frequency than the kfrequencyat which said oscillatory circuit oscillates, a linear inductor in saiddischarge circuit, a space discharge tube in said discharge circuit, avibrator for timing the discharge of said tube to control the dischargeof said first condenser through said discharge circuit, and means toderive an alternating output current from said oscillatory circuit.

6. An inverter comprising a source of voltage, a pair of condensers inseries connected across said source of voltage, an oscillatory circuitcomprising a condenser and a saturable inductor, discharge circuits foralternately discharging said pair of condensers through said oscillatorycircuit, a controlled ignition discharge tube in each of said dischargecircuits for causing said pair of condensers to discharge, a linearinductor common to both of said discharge circuits, means for timing theignition of said discharge tubes to control the discharge of said pairof condensers through said discharge circuits, and means to derive analternating output current from said oscillatory circuit.

'1. An inverter comprising a source of voltage, a pair of condensers inseries connected across said source of voltage, an oscillatory circuitcomprising a condenser and a saturable inductor, discharge circuitstuned to a higher frequency than said oscillatory circuits foralternately discharging said pair of condensers through said oscillatorycircuit, a controlled ignition discharge tube in each of said dischargecircuits for causing said pair of condensers to discharge, a linearinductor common to both of said discharge circuits, means for timing theignition of saididischarge tubes to control the discharge of said pairof condensers through said discharge circuits, and means to derive analternating output current from said oscillatory circuit. 8.. Aninverter comprising a source of voltage, a pair of condensers in seriesconnected across said source of voltage, an oscillatory circuitcomprising a condenser and a saturable inductor, discharge circuits foralternately discharging said pair of condensers through said oscillatorycircuit, a linear inductor common to both of said discharge circuits, apair of space discharge tubes one in each of said discharge circuits,means for timing the discharge of said tubes to control the discharge ofsaid pair `oi? condensers through said discharge circuits, and means toderive an alternaing output current from said oscillatory circu 9. Aninverter comprising a source of voltage, a pair of condensers in seriesconnected across said source of voltage, an oscillatory circuitcomprising a condenser and a saturable inductor, discharge circuits foralternately discharging said pair of condensers through said oscillatorycircuit, a linear inductor common to both of said discharge circuits, apair of space discharge tubes one in each of said discharge circuits, avibrator for timing the discharge of said discharge tubes to control thedischarge of said pair of condensers through said discharge circuits,and means to derive an alternating output current from said oscillatorycircuit.

10. An inverter comprising a source of voltage, a pair of condensers inseries connected across said source of voltage, an oscillatory circuitcomprising a condenser and a saturable inductor, discharge circuits foralternately discharging said pair of condensers through said oscillatorycircuit, a linear inductor common to both of said discharge circuits,said discharge circuits being tuned to a frequency higher than thefrequency at which said oscillatory circuit oscillates, a pair of spacedischarge tubes one in each of said discharge circuits, a vibrator fortiming the discharge of said discharge tubes to control the discharge ofsaid pair of condensers through said discharge circuits, and means toderive an alternating output current from said oscillatory circuit.

HANS KLEMPERER.

REFERENCES CITED The following references are of record in the file ofthis patent:

